There is a need for an economical ink suitable for printing on paper towels, facial tissues, toilet tissues, and the like which has such desirable properties as being stable to water and detergents, non-irritating to the skin, non-toxic, and capable of being bleached by chlorine at the sewage treatment plant or at the paper mill whereby waste towels and tissues printed with such inks may be recovered for recycling. It is also desirable that the ink be noncorrosive to thereby extend the life of printing presses and printing plates.
Prior art inks for printing on paper products such as towels and tissues often have a number of the foregoing deficiencies. For example, inks which derive their color from pigments are generally not chlorine bleachable, hence difficulty is experienced in recycling the printed paper or in treating it at the sewage treatment plant. Some inks are run on the press in acidic media, thereby causing corrosion of metal parts and producing tackiness on natural rubber printing plates. Other inks may irritate the skin or be adversely affected by water or detergents.